The present invention is related to single-chip LED lamps. The purpose of the invention is to provide a single-chip LED lamp that is up to 250 times more powerful than a conventional single-chip LED lamp.
Existing single-chip LED lamps are generally of low input power, typically 40-150 milliwatts. There has been a need for a long time for a single-chip LED lamp of higher power, for example 1 watt or more. The need for a higher power single-chip LED lamp has not been met in spite of the fact that an enormous amount of effort has gone into improvement of LED devices. The amount of effort that has gone into improvement of LED devices is evidenced by the fact that international class H01L 33/00, which is devoted to improvement of LED devices, has thousands of patent publications all differing in disclosure.
Designers of lamps for outdoor use have had the choice mainly of incandescent tungsten light sources, gas discharge light sources, and LED light sources. Designers of LED-based lamps requiring high power have had to resort to using clusters of single chip LED lamps, each of about 0.1 watt rating, wired in series or in parallel and housed together as a single lamp unit to achieve enhanced power. Providing a lamp unit by clustering single-chip LED lamps is very costly, since it involves making several single-chip lamps, housing them in a unit, wiring them up, and testing the final unit. U.S. Pat. No. 5,382,811 and 5,632,551 provide examples of cluster lamps.
Applications for high power LED lamps include outdoor displays, which usually have to operate in direct sunlight and so require powerful lamps, and vehicle lights and traffic lights. At present long-life LED traffic lights for use at street intersections need more than a hundred conventional single-chip LED lamps for each lamp unit. The need to use many LED lamps to provide a single LED traffic light is a disadvantage, particularly since only one tungsten light source is needed for a conventional traffic light.
Prior art single-chip LED lamps having clear convergent lenses, used widely in outdoor displays, suffer not only from the fact that they are of low power but also from the fact that they project light that is not uniform. The non-uniformity is partly due to the bonding pad or pads on the chip top face, which are projected by the lamp as dark areas. The typical width of the bonding pad is about 30-40% of the width of the chip and this is large enough to interfere with achieving good uniformity of projected light even if the LED lens is defocussed relative to top face of the chip. For good quality image displays it is desirable to match the apparent brightnesses of the lamps to within 5%. To achieve this it is important to reduce the nonuniformity caused by the bonding pads.
An object of the present invention is to provide a single chip LED lamp that avoids or reduces the need for clustering.
A further object of the present invention is to provide a single chip LED lamp arranged so that light emitting portions of the chip are adjusted to be equalised in intensity.
A further object of the present invention is to provide a single chip LED lamp in which the sizes of the bonding pads relative to the size of the chip are reduced, so as to improve uniformity of light projected by a lensed lamp.
A further object of the present invention is to provide a single chip LED lamp, with input power in the region of 5-25 watts, that has low rise of the junction temperature when energised, thus prolonging the life of the lamp and reducing or eliminating the need for forced ventilation of the lamp.
A further object of the present invention is to provide a single chip LED lamp arranged so that light emitting portions of the chip that are faulty by short-circuit are automatically starved of electrical power.
According to an aspect of the invention an LED light source suitable for an LED lamp includes an LED chip having a top face and comprising a substrate and semiconductor layers between the top face and the substrate, the semiconductor layers forming the core of a light guide extending parallel to the plane of the top face. The chip includes at least one cavity with light-emitting side walls that extends into at least one of the semiconductor layers. The chip converts guided light in the core into top light. According to another aspect of the invention guided light in the core is extracted with the aid of reflectors that are parallel to the semiconductor layers. According to yet another aspect of the invention metal tracks connected to the n-type semiconductor layer are provided that enhance the efficiency of the lamp.
According to another aspect of the invention an LED light source includes a chip comprising at least two light emitters each having a triangular top face, the two emitters being separated by a trench.
According to another aspect of the invention a single chip LED lamp which can have input power of 5-25 watts includes an LED chip having a top face and comprising a substrate and semiconductor layers between the top face and the substrate, the semiconductor layers forming the core of a light guide extending parallel to the plane of the top face. The chip includes at least one trench, and a heat sink is attached to the top face of the chip that draws heat from the active region of the chip.
According to another aspect of the invention an LED light source has an LED chip with a plurality of individually powered light emitting elements each provided with a fuse. This improves the yield of usable LED chips during manufacture.